Point-based or line-based train influence is used for controlling railroad operations. In point-based train influence, limited amounts of specific information items at fixed-position influencing devices is transmitted to vehicles moving past the devices. The information items may be evaluated, and if necessary, processed further at the device. In line-based train influence, more information can be exchanged for greater vehicle control and monitoring. Information can be continuously transmitted from a section of the track to the vehicles and, if necessary, in the opposite direction. Information is normally transmitted by means of linear conductors laid in the track, to which at least individual vehicles of the trains passing through that section are inductively coupled. Due to the complexity of installation, the operation and maintenance of the linear conductors laid in the track is considerable. For this reason, the prior art contemplates data which is transmitted between the individual subscribers by radio. A mobile radio system can be used for this purpose, as is already used for voice and data transmission and is described in EP 0 726 689 A2. The data to be transmitted for controlling railroad vehicles is, in contrast to voice radio data, safety-relevant since it affects the vehicle control directly. Care must therefore be taken in a suitable way to ensure that the data cannot be corrupted or lost on their way from the data source to the data sink. Cryptographic methods are nowadays widely used for the security of such data.
One special feature of railroad operation is that the data to be transmitted to the trains are produced in a decentralized manner by individual control stations or control points. Data transmitted via linear conductors to a train is typically linked to a single control point and, on entering a subsequent section region, is automatically changed over to the control point responsible for that section. With radio train influencing, this automatic association, which is dependent on the decentralized features of the rail system, with the respectively responsible control point is no longer provided. In fact, the vehicle or the control point responsible for the vehicle for this purpose, and on the basis of the known location of the vehicle on the section, either has to request the control center set up a link to the train which is approaching its section region, or cause the vehicle to set up this link. A specific time interval in the order of magnitude of up to 10 s is in each case required for this purpose. In this time, the locomotive of a train is still linked to the control center of the section region over which it is travelling and is thus busy with setting up a link to the control center of the next region. The vehicle needs to have at least two radios for this purpose.
One very major problem with regard to data transmission in decentralized systems, such as railroad systems, is also presented by the central services, for example those for disposition and central diagnosis. Special radio channels are either provided for these central services, although this is scarcely feasible owing to the limited resources, or else these central services communicate with the trains via the communications modules of the decentralized controllers. In the latter case, however, the link between the central services and the trains must be continuously readjusted to match the current locations of the trains. That is, the data for the central services have to be continually switched to the communications modules of the adjacent control centers. This results in gaps in the transmission of data, in particular due to synchronization processes, in the order of magnitude of several seconds. Furthermore, a disadvantage of this constellation is that central services which are making a request to a vehicle must first of all determine which control center is currently linked to the relevant vehicle.
In a central communications device according to DE 197 21 246, these disadvantages are avoided by introducing an additional central gateway computer which allows a continuous link to the trains, which are permanently assigned to the gateway computer. The change in the link to the decentralized objects in this case takes place only on the fixed side between the gateway computer and the decentralized object. The accessibility of mobile and fixed objects is in this case provided by a fixed relationship between the mobile object and the gateway computer.
This solution has the disadvantages of long communications paths between mobile and fixed objects due to the introduction of a fixed-position central gateway computer, via which the communication with the mobile subscriber takes place irrespective of its location. Furthermore, the relationships between the mobile objects and the gateway computers associated with them have to be set up and maintained in the vehicle and in the fixed-position gateway computer.
In summary, problems with the known prior art are that, in solutions based on the decentralized solution approach, central objects have the problem of determining those decentralized objects which have a link to the train, in order to connect to this link. Unknown mobile objects cannot be accessed using this method since no information is available about their location in the fixed-position objects. When the responsible decentralized object changes, a new link is set up to the next decentralized object. A second mobile radio is required to do this. All the links of the central objects must likewise be changed to the new radio link (hopping).
In implementations based on the central solution approach, each train has a fixed substitute in a gateway computer on the section side (fixed relationship between the mobile object and the gateway computer). Consequently, calls and data always have to be passed via a fixed-position node, irrespective of where the train is located. The resultant communications paths are consequently long, resulting in high operating costs. Furthermore, the substitute relationships to the mobile objects have to be configured and maintained individually in each gateway computer and each mobile object, which leads to high engineering and maintenance costs.